Department of Biochemistry and Molecular Biophysics
Kansas State University
Metabolic defects promote pathogenesis in a muscular dystrophy model (2018-2019)
Muscular dystrophies are a heterogeneous group of myopathic disorders characterized by the progressive degeneration of skeletal and cardiac muscle. One type of dystrophy that leads to muscle weakness and a loss of muscle strength is called Limb-Girdle Muscular Dystrophy type 2H (LGMD2H).
LGMD2H is caused by a mutation in the E3 ubiquitin ligase protein TRIM32. Diverse TRIM32 substrates have been identified in cell cycle regulation, neuronal differentiation, muscle physiology, and tumorigenesis. The generation of a Trim32-/- knockout mouse was a key advance in studying LGMD2H muscle degeneration. However, the ubiquitous expression of TRIM32 and pleiotropic phenotypes present in these mutant mice did not clarify the role of TRIM32 in LGMD2H pathogenesis. For these reasons, it is clear that alternative models are needed to fully understand the muscle-intrinsic role of TRIM32.
We were the first group to publish a Drosophila model for LGMD2H. Mutations in thin (tn), which encodes for Drosophila TRIM32, exhibit a degenerative muscle phenotype and are defective in locomotor ability. These features recapitulate the histological and mobility defects present in LGMD2H patients. TRIM32 is characterized by an N-terminal RING domain and C-terminal NHL repeats. Pathogenic alleles that cause LGMD2H are located within the NHL region, which is predicted to mediate protein interactions. It has already been reported that the NHL domain prevents muscle degeneration in our Drosophila LGMD2H model. Using a proteomics approach to identify proteins that physically interact with the NHL domain, we find that TRIM32-NHL binds to glycolytic proteins. Moreover, loss of Drosophila TRIM32 alters the subcellular localization of these enzymes. The overall objective of the proposed research is to use our Drosophila LGMD2H model to determine if disease-causing point mutations in TRIM32 alter ubiquitin signatures that ultimately affect overall protein levels and/or subcellular localization of glycolytic enzymes in muscle tissue.